1. Field of the Invention
The present invention relates to optics. More specifically, the present invention relates to corrective optical elements used in conjunction with conformal windows and complex domes for protecting optical sensors.
2. Description of the Related Art
Optical sensors are employed in a variety of systems that are deployed into a variety of environments. Electro-optic sensors are commonly used, and may be designed to be sensitive in a variety of wavelengths, including visible light, near infrared, long infrared, as well as other wavelengths. Optical sensors are typically structured to detect energy along a focal plane onto which a real image is formed by an optical system placed between the focal plane of the sensor and some object field in the distant environment. Various operating environments are encountered, including air, water, fluids, chemicals, bodily fluids, and as well as other environments. For example, a guided missile operates in an ambient air environment and might employ a near infrared electro-optical sensor with an image field corresponding to distance objects in the environment, such as enemy aircraft. In another example, a submersible research vehicle might employ a visible light sensor that operates in seawater.
Electro-optical sensors typically cannot endure direct exposure to the environment in which they operate, so designers place an optical window between the sensor and the environment to protect the sensor. The optical window thus becomes an element of the optical system used with the sensor. Naturally, the optical system used with an optical sensor is a major factor in the resolving power and performance of the overall system. System designers often seek high optical performance. In order to minimize the optical aberrations that are contributed by the optical window, designers have typically chosen simple optical configurations for these windows, most commonly flat plates or hemispherical domes.
There are other considerations in system designs that employ electro-optical sensors with optical windows. For example, in the case of a missile, the aerodynamics of the missile in flight is of critical importance in the effectiveness of the missile system as a whole. The same is often true in other systems, including torpedoes, chemical process sensors, blood vessel sensors, and many other systems. In the case of a missile, the electro-optic sensor is preferably placed at the nose of the missile, which shape has a great effect on aerodynamic drag. A flat plate window is a poor aerodynamic choice, a hemispherical window is better, but an elongated shape is preferred to improve the drag coefficient of the missile. In other applications, such as where a sensor ‘looks’ out the side of a system built into a complex shaped enclosure, designers prefer that the optical window conform to the shape of the system enclosure. Such an optical window is called a conformal optical window.
The problem with complex shaped optical windows is that they induce optical aberrations that must be corrected in order to maintain high optical performance of the sensor system. What this has meant in the prior art is that systems designers have had to add one or more optical corrector elements to counteract the aberrations induced by the window. The window behaves as a lens, which refracts light according to the shape of the window, the indices or refraction of the window, the environment itself, and other components in the optical system in the sensor. While technology exists for building complex shaped windows and corresponding optical corrector elements, they are difficult to design, add to system cost, as well as increasing development time and effort. Thus, there is a need in the art for a systems and method for reducing the aberrations and deleterious effects of conformal and complex shaped optical windows used with optical sensors.